1. Field of the Invention
The present invention relates to a double-sided meshing type silent chain having meshing teeth on both inner and outer peripheral sides thereof for mesh with teeth of sprockets.
2. Description of the Related Art
Conventionally, as a timing chain used for transmitting rotation of an engine crankshaft to a cam-shaft or a shaft of an auxiliary device such as an oil pump, there is known a double-sided meshing type silent chain having meshing teeth on both inner and outer peripheral sides thereof so that the meshing teeth on the inner peripheral side of the chain rotate sprockets mounted to the crankshaft and camshaft, respectively, and the meshing teeth on the outer peripheral side of the chain rotate a sprocket mounted to the shaft of the auxiliary device (Japanese Patent Laid-open Publications Nos. HEI-11-166600 and HEI-11-257439).
When the known double-sided meshing type silent chain is wound around a driving sprocket mounted to an engine crankshaft, a first driven sprocket mounted to a camshaft of an intake valve mechanism and a second driven sprocket mounted to a camshaft of an exhaust valve mechanism, the meshing teeth on the inner peripheral side of the chain mesh with the respective teeth of the driving and driven sprockets. Thus, all the sprockets rotate in the same direction. In the case where the meshing teeth on the outer peripheral side of the chain mesh with a sprocket mounted to the shaft of an auxiliary device such as an oil pump disposed on the outer peripheral side of the chain, the sprocket of the auxiliary device rotates in a direction opposite to the direction of rotation of the driving sprocket mounted to the crankshaft (Japanese Utility Model Registration No. 2553206).
FIGS. 13 and 14 show one example of the conventional double-sided meshing type silent chains. As shown in these figures, the double-sided meshing type silent chain 51 includes a plurality of interleaved link plates 55, 56 each having a pair of meshing teeth 52 and a pair of pin-accommodation holes 53, the link plates 55, 56 being connected with one another by connecting pins 57 in an endless fashion in such a manner that the meshing teeth 52 project from both inner and outer peripheral sides of the chain 51. The link plates 55, 56 have a flat back surface 54 on a side thereof which is opposite to the front side on which the meshing teeth 52 are formed.
The link plates 55, 56 are oriented such that the meshing teeth 52 of plural laminated inner link plates 55 located centrally in the width direction of the chain 51 project inwardly with respect to the chain 51, and the meshing teeth 52 of two adjacent outer link plates 56 located at each end in the width direction of the chain 51 project outwardly with respect to the chain 51. An outermost one of the outer link plates 56 which is located at each widthwise end of the chain 51 has pin-accommodation holes 53 in which connecting pins 57 are press-fit.
A sprocket used for mesh with the meshing teeth 52 projecting inwardly from a central portion of the chain 51 comprises a general sprocket 64 (FIG. 17) which is designed for mesh with a single-sided meshing type silent chain. In FIG. 17, numeral 65 denotes teeth of the sprocket 64, and numeral 66 denotes a shaft on which the sprocket 64 is mounted.
Another example of the conventional double-sided meshing type silent chain is shown in FIGS. 20 and 21. The double-sided meshing type silent chain 68 is composed of inner link plates 55 and outer link plates 56 in a like manner as the silent chain 51 shown in FIGS. 13 and 14. The silent chain 68 is, however, different from the silent chain 51 in that connecting pins 57 are rotatably fit in the pin-accommodation holes 53 in the outermost link plates 56 located at opposite widthwise ends of the chain, and retainer rings 69 located outside the outermost link plates are firmly secured to the connecting pins 57 for preventing removal of the connecting pins 57.
When the conventional double-sided meshing type silent chains 51, 68 are wound around the driving sprocket on the engine crankshaft and the respective driven sprockets of the intake and exhaust valve mechanisms as previously described, one side which is in contact with these sprockets is an inner peripheral side of the silent chain, and the opposite side which is in contact with another sprocket mounted on the shaft of auxiliary device located outside the silent chain is an outer peripheral side of the silent chain.
The conventional double-sided meshing type silent chain shown in FIGS. 13 and 14 has a problem that since the connecting pins 57 are press-fit in the pin-accommodation holes 53 of the outermost link plates 56, when the outer link plates 65 are used for driving the sprocket of the auxiliary device shaft, the strength of the outermost link plates 56 is greatly reduced at an inner peripheral portion extending around each pin-accommodation hole 53 by the effect of a stress which is exerted on the winner peripheral surface of each pin-accommodation hole 53 when the meshing teeth 52 of the outermost link plates 56 collide with the teeth of the sprocket at the onset of meshing engagement, and a tensile stress which has been created in the inner peripheral portions of the pin-accommodation holes 53 of the outermost link plates due to press-fit connection with the connecting pins 57. The mechanical strength of the silent chain is considerably reduced.
The outermost link plates 56 undergo deformation or swelling occurring complicatedly in the radial direction of the connecting pins 57 when the connecting pins 57 and the pin-accommodation holes 53 are press-fit with each other. This makes it difficult for an engagement surface, such as an inside flank or an outside flank of meshing tooth, to keep a desired profile. Since the meshing accuracy is an important requirement for the silent chain, design of the silent chain should be done with the foregoing deformation of the outermost link plates 56 taken into consideration.
A sprocket 61, which meshes with the meshing teeth of the outer link plates 56, supports side surfaces of every other inner link plates 55 in the longitudinal direction of the chain. This may deteriorate the traveling stability of the chain, allowing widthwise vibration and twisting of the chain to occur.
When the teeth 52 of the outer link plates 56 and the teeth 62 of the sprocket 61 mesh with each other on the outer peripheral side of the double-sided meshing type silent chain 51, meshing at a portion of the chain 51 located on a line Axe2x80x94A shown in FIG. 14 occurs in a manner shown in FIG. 15, in which the inner link plates 55 (indicated by hatching) located next to the outer link plates 56 are in slide contact with opposite inside surfaces of the sprocket 61 to thereby guide the travel of the chain. However, at a portion of the chain 51 located on a line Bxe2x80x94B shown in FIG. 14, meshing occurs in a manner as shown in FIG. 16, in which the inner link plates 55 located next to the outer link plates 56 are not in slide contact with the opposite inside surfaces of the sprocket 61. This may allow the chain to vibrate in the width direction thereof, thereby deteriorating the traveling stability of the chain. In FIGS. 15 and 16, numeral 63 denotes a shaft of the sprocket 61.
Even when a shoe 67 of a chain tensioner or of a guide member is disposed on a back surface side of the outer link plates 56 for guiding the chain, as shown in FIGS. 18 and 19, portions of the silent chain 51 located on the lines Axe2x80x94A and Bxe2x80x94B of FIG. 14 are guided in such a manner as shown in FIGS. 18 and 19, respectively, in which only one of two adjacent outer link plates (indicated by hatching) is in sliding contact with the shoe 67 at each widthwise end of the chain. This arrangement increases surface pressure acting on the shoe 67, thereby accelerating wear of the shoe 67.
In the conventional double-sided meshing type silent chain 68 shown in FIGS. 20 and 21, since the outermost link plates 56 located at opposite widthwise ends of the chain are rotatably fitted with the connecting pins 57 with the retainer rings 69 provided to prevent removal of link plates 55 from the connecting pins 57, abrasive wear occurs due to relative rotation or pivotal movement between the pin-accommodation holes 53 of two adjacent rows K and C of interleaved link plates 55, 56 and the connecting pins 57, resulting in undue wear elongation of the silent chain 68. Additionally, since the retainer rings 69 do not act as a strengthening member capable us sustaining a chain tension, the strength of the silent chain 68 shown in FIGS. 20 and 21 is smaller than a silent chain having the same width.
An object of the present invention is to provide a double-sided meshing type silent chain which solves the above-mentioned problems involved in the related art, is capable of avoiding a reduction in strength caused due to press-fit connection between the outer link plates with meshing teeth and the connecting pins, thereby obtaining a greater strength than a conventional chain of the same width equipped with retainer rings, is able to improve the traveling stability of the chain when the meshing teeth of the outer link plates and teeth of a sprocket mesh with each other on an outer peripheral side of the chain, can reduce surface pressure per unit link plate to thereby minimize wear on a shoe when the shoe is in slide contact with the back surfaces of the outer link plates on the inner peripheral side of the chain, and is able to suppress elongation of the chain caused due to abrasive wear of the pin-accommodation holes and the connecting pins.
To achieve the above object, according to the present invention, there is provided a double-sided meshing type silent chain comprising: a plurality of interleaved rows of link plates articulately connected with one another by connecting pins, each of the link plates having a pair of meshing teeth formed on one side thereof, a flat back face formed on the opposite side thereof, and a pair of pin-accommodation holes rotatably receiving therein a pair of connecting pins, respectively, of the connecting pins. The link plates in each link plate row are composed of at least one pair of outer link plates disposed in opposite end portions, respectively, in the width direction of the chain, and a plurality of inner link plates disposed in a central portion in the wise direction of the chain disposed between the end portions. The inner and outer link plates are oriented such that the meshing teeth of the inner link plates project from one peripheral side of the chain and the meshing teeth of the outer link plates project from the opposite peripheral side of the chain. The chain further has guide plates located outside the row of link plates in the width direction of the chain. Each of the guide plates has a flat back face formed on one side thereof and a pair of pin-accommodation holes formed therein, the pin-accommodation holes being press-fit with the connecting pins.
It is preferable that the flat back faces of the outer link plates and the flat back faces of the guide plates lie flush with each other.
With this arrangement, since the outer link plates are not secured by press-fitting with the connecting pins as in the conventional chain but serves as a strengthening member of the chain. The chain has a greater strength than a conventional chain of the same width equipped with a retainer ring attached to opposite ends of each connecting pin to prevent removal of the pins from the link plates. When the chain is used with a sprocket disposed on an outer peripheral side of the chain, the guide plates are brought into sliding contact with opposite end faces of the sprocket, so that the chain can travel stably without causing lateral oscillation. When the chain is used with a guide member or a chain tensioner disposed on the inner peripheral side of the chain for sliding engagement with the flat back faces of the outer link plates, the flat back faces of the guide plates slidably engage a shoe of the guide member or chain tensioner concurrently with the flat back faces of the outer link plates.